Chain saw drive sprocket



Nov. 28, 1967 J. F. WRIGHT' 3,354,737

CHAIN SAW DRIVE SPROCKET Filed May 27, 1965 Jesse F. Wr/yfif INVENTOR.

zww/d I Arivc" K S United States Patent 3,354,737 CHAIN SAW DRIVESPROCKET Jesse F. Wright, P.O. Box 284K, Rte. 5, Lufkin, Tex. 75901Filed May 27, 1965, Ser. No. 459,167 3 Claims. (Cl. 74-243) ABSTRACT OFTHE DISCLOSURE A drive sprocket for a chain saw having driving pinsengaging the chain at the cutting links and their associated connectinglinks.

This abstract is neither intended to define the invention of theapplication which, of course, is measured by the claims, nor is itintended to be limiting as to the scope of the invention in any way.

This invention relates generally to power chain saws and moreparticularly to a sprocket driving means adapted for use with a standardsaw chain in a power chain saw.

The usual power chain saw includes an endless link chain having cutterelements projecting outwardly and also having driving or pulling lugs orprojections directed inwardly. The driving or pulling lugs are shapednot only to coact with a driving element, such as a toothed sprocket,but also to guide the chain in its longitudinal movement by theirengagement within the groove of a guide bar. Because the saw isportable, it is desirable to hold size and weight to a minimum and forthis reason the driving element for the endless chain is of as small adiameter as possible. This means that the circumferential path traversedby the chain as it passes around the driving element is along arelatively small radius with the result that the inwardly directeddriving or pulling lugs on the chain move into relative proximity toeach other during this portion of travel. Because of the relativelysmall spacing between the driving lugs, a toothed sprocket is employedas the driving element since it may have its teeth tapered in suchmanner that adequate driving connection :between the sprocket and chainmay be effected without undue binding as said chain moves through thecircumferential path of relatively small radius.

The toothed drive sprocket has been found satisfactory insofar aspermitting the use of a small diameter driving element is concerned butsuch sprocket has the disadvantage of excessive wear and thereforerelatively short life. Such excessive wear is caused by the excessivefrictional sliding contact between the sides of the sprocket teeth andthe driving or pulling lugs of the chain. Actual experience has shownthat the usual drive sprocket must be constantly replaced in arelatively short time.

Other types of driving means have been attempted, particularlyroller-type driving sprockets, which eliminated friction because of thefreedom of movement but these types have the disadvantage of beingcomparatively large and heavy.

It is therefore an object of this invention to provide an improvedsprocket driving means for a power chain saw in which the device isrelatively light and has minimum weight and friction and further coactswith a standard saw chain to transmit the movement from a prime mover tothe chain.

Another object of the present invention is to provide a new and improvedfree pin-type sprocket drive for a chain saw being adaptable to drive astandard saw chain with a minimum of friction thereby minimizing wear.

A further object of the present invention is to provide a drive sprocketfor a power chain saw having free pin engagement with the links of thesaw chain for driving the saw chain and further providing an annulargroove defined by shoulders whereby the guiding links of said chain areguided and partially supported in said groove.

Still another object of the present invention is to provide a drivesprocket for a power chain saw having pins engaging the saw chainwherein such pins are readily removable.

A further object of the present invention is to provide a drive sprockethaving pins for engagement with the saw chain positioned loosely in thesprocket whereby pin wear is uniform.

These and other objects of the present invention, together with theconstruction designed to carry out the invention, will be hereinafterdescribed, together with other features thereof.

The invention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, wherein an example of the invention is shown,and wherein:

FIGURE 1 is a side elevation of a portable powered chain saw;

FIGURE 2 is an enlarged fragmentary view, partly in section, of thedrive sprocket and saw chain and associated parts;

FIGURE 3 is a sectional view taken along line 33 in FIGURE 2; and

FIGURE 4 is a cross-sectional view of another form of drive sprocket ofthe present invention.

In the drawings the letter A generally designates a portable chain sawwhich includes a prime mover, such as internal combustion engine 10having suitable handles 11 attached to the outer casing thereof. Theengine 10 is suitably connected to the drive sprocket 12, as hereinafterdescribed in detail, and said sprocket is in driving engagement withportions of the saw chain 13. A guide bar 14, which may be constructedof metal or other materials, extends forwardly from the drive sprocket13 and may have its outer end rounded to a semicircular form asindicated at 14a. The endless saw chain 13 passes over the drivingsprocket 12 and extends around the edge of the guide bar 14, and uponrotation of the sprocket, said chain is moved in a path around the guidebar.

The saw chain 13 used with the present invention is provided withcutting elements or links 15, guiding elements or links 16 andconnecting elements or links 17. The cutting links 15 are provided withthe usual teeth which do the direct cutting and contact work duringoperation. It should be noted that the saw chain 13 as illustrated is astandard saw chain which is readily available on the market. The innerside of the connecting links 17 and the cutting links 15 is providedwith the arcuate recess 18 which normally would receive the outermostportion of a driving sprocket tooth. However, in the present invention aplurality of pins 19 are mounted in the drive sprocket 12 for engagementwith the chain at the position defined by the recess in the links. Thus,approximately one-half of the circumference of the driving pins 19 isreceived in the recess 18. The driving pins 19 additionally contact thetrailing edge of the guiding links 16.

The drive sprocket 12, as shown in FIGURE 3, includes the main body 20having a central bore 21 to receive a drive shaft 22 therethrough. Thesprocket body 20 is provided with radially extending flanges 22 and 23which initially define the annular groove 24 into which the inwardlyprojecting portion of the guiding links 16 extends. The flanges at theouter portion of the groove 24 form the slightly tapered shoulders 25and 26 and extend radially outwardly therefrom in parallel relationshipto each other to define a larger groove 27 beyond the shoulders 25 and26. The flange 23 is extended outwardly at its rearward portion, as at28, and terminates in cylindrical section 29 which is substantiallyhollow as shown I for the reasons hereinafter more fully explained.

Holes 30 are drilled in an axial direction through flange 22 and intoflange 23 terminating short of the rearmost portion of flange 23. Theholes 30 are positioned radially outward. from the center of the body 28and are spaced circumferentially therearound as best illustrated in FIG-URE 2. The holes 30 are substantially perpendicular to the parallelsurfaces defining the larger groove 27 for the reasons hereinafter morefully explained. The diameter of each of the holes 30' is preferablyslightly larger than the diameter of the pins 19 to allow the pins 19 acertain degree offreedom of movement when positioned in holes 30. Suchfreedom of movement will prevent the accumulation of wear on the pins 19at particular points by distributing the wear uniformly around the pins.The holes 30 extend through flange 22 and allow the pins 19 to beinserted therein from the face 31 of the flange 22. Retaining means,such as annular cover plate 32, is secured to the face 31 of the flange22 by a plurality of screws 33 to retain the pins 19 in the holes 30.Thus, when a saw chain 13 is in operational engagement with the drivesprocket 12, the pins 19 extend from flange 22 to flange 23 to be ableto engage within the recesses 18 of the links and against a portion of atrailing edge of the guiding links 16.

With the drive sprocket 12 positioned on the shaft 22, washer 34 will bepositioned over the threaded end of the shaft 22 and engage in therecess portion 35 on the face 31-, and nut 36 will engage the threadedendof shaft 22 to secure drive sprocket 12 in position thereon. Withinthe interior of the cylindrical section 29 is positioned a clutchassembly 37. Since drive sprocket 12 is not keyed or in any way fixedlysecured to the shaft 22, the clutch assembly 37 is provided to transmitthe rotation of the shaft to the drive sprocket whereby the saw chainwill be driven. The clutch assembly 37 includes the clutch segments 38,theclutch spring 39 and the clutch collar 40. The individual clutchsegments 38 are positioned in the recesses in the clutch collar 49. Theclutch collar 40 is secured to the shaft 22 by the key 42. The springs39 engage in the grooves 45 in each of the segments 38 whereby saidsegments 38 are urged to a position against the bottom of the recess inthe collar 40.

Rotation of the shaft 22 by the prime mover will rotate the collar 40 bythe direct engagement of'key 42 between the shaft 22 and the collar 40.Rotation of the collar 40 causes clutch segments 38 to rotate, and thecentrifugal force created will tend to move the clutch segments 38radially outwardly against the restraining force of the spring 39. Whenthe speed of rotation of the clutch assembly 37 is sufiicient to createcentrifugal force moving clutch segments 38 to a position wherein theirouter'surface engages the surface 44 on the interior of cylindricalsection 29, the drive sprocket 12 will be then rotated. At any time thatthe speed of rotation of the clutch assembly 37 is decreased to a pointwhere the spring force overcomes the centrifugal force, the clutch willdisengage by the radial inward movement of clutch segments 38 and thedrive sprocket 12 will no longer be rotated.v

In FIGURE 4 a modified form of drive sprocket, designated 47, is shown.The drive sprocket 47 is keyed to the shaft 48 by the key 49 and issecured thereon by the washer 50 and the nut 51 threadedly engaging thethreaded end of the shaft 48. The drive sprocket 47 is provided with tworadially extending flanges 52 and 53 which de fine an inner groove 54 atthe upper end of which the flanges form the shoulders 55 and 56. Flanges52 and 53 extend outwardly beyond the shoulders 55 and 56 to define anenlarged groove 57. Holes 58 which receive the pins 59 extend throughthe flange 53 from its face 60 and partially through the fiange'52.Retaining means, such as snap ring 61, is secured in coveringrelationship to the face 60 by engagement with the groove 62 formed onflange 53 to retain the pins 59 in the holes 58.

In operation when the drive sprocket 12 is rotated through the clutchmechanism 37, the pins 19 engage in the recesses, 18 and partiallyagainst the trailing edge of the guiding link 16 to move the saw chain13 around the guide bar 14. The central portion of the pins 19 engagesthe guiding link 16 while portions on each side of the central portionof the pins 19 engage in the recesses 18. While the pins 19 arerelatively small in diameter, they do have a substantial area of drivingengagement with the saw chain 13. Because of the looseness of the pins19 in the holes 30, the pins 19 will be easily rotated to minimize wearand friction.

Because of the vertical faces of the groove 27 and the perpendicularrelationship between such faces and the holes 30, the amount of dirt andtrash which can Work into the space between the pins 19 and the holes 30is minimized. The accumulation of any dirt or trash in the space betweenthe pins 19 and the holes 30 will restrict the freedom of movement ofthe pins 19. It has been found that the perpendicular relationshipbetween the faces of the secondary groove 27 and the axes of the holes30 provides the very minimum of dirt collection. The restriction of thefreedom of movement of the pins 19 in the holes 38 will greatlyaccelerate wear on the pins and require their early replacement.

The operation of drive sprocket 47 illustrated in FIG- URE 4 issubstantially the same as the operation of drive sprocket. 12 exceptthat sprocket 47 is keyed directly to the shaft 48 by the key 49 anddoes not include a clutch assembly. In drive sprocket 47 the pins 59 areslightly smaller than the holes 58 in which they reside to allow thepins freedom of rotation therein to minimize friction. The axes. of theholes 58- are substantially perpendicular to the faces of the largergroove 57 to limit the accumulation of trash or dirt in the holes 58.

Since the only point of wear in the drive sprockets of the presentinvention is the pins, both forms of drive sprocket have provision madefor quick and easy replacement of the-pins. In FIGURE 3 the pins 19 areretained in the holes 39 by the retainer ring 32 which is secured to theface 31 of sprocket 12 by the screws 33. In FIG- URE 4 the pins-59 areheld in the holes- 58 by the snap ring 61 which is readily removed fromengagement with the groove 62. Thus, the pins are readilyreplaceable inboth forms of the invention. The pins may be removed from the outer sideof the sprocket, as shown in FIGURE 3, or from the innerside of thesprocket, as shown in FIGURE- 4-. Itis contemplated that the number ofpinreceiving holes provided in each sprocket could be doubled so that achange of holeswould be available in the eventthe' holesbecame worn orotherwise limited the freedornof movement of the pins.-The freedom ofmovement of the pins inall forms of the present invention Will greatlyminimize friction and therefore reduce wear on the pins.

Itv should be noted: that the grooves 24' and 54 will engage theinnermost projection of the links 16 and will maintain the positionofthe chain even when the saw is operating on its side. Without thisengagement it would be possible for the chain to'rnove to one side orthe other of. the sprocket to cause extreme Wear, and without theoutward extension of the flanges above the wider grooves 27- and 57-occasionally the chainwould become completely disengaged from thesprocket. The grooves 24 and 54 will prevent the extra wear by guidingthe saw chain in its'movement around the driving sprocket.

As shown in the drawings, the guide links are positioned sufficientlyclose to the. bottom of the grooves so that they receive support fromthe groove in the event a pin should fail.

The operation of all' forms of the drive sprocket of the presentinvention, however, provide the engagement between the drive pins whichare loosely positioned in the drive sprocket with the recesses in thecutting and connecting links of the chain saw and with the back edge ofthe guiding links. The drive sprocket provides a relatively light weightand small driving element for a chain saw whichhasreduced friction andwear. The drive sprocket will coact with a standard saw chain to providethe means of transmitting the rotation to the saw chain from the shaftwhich connects to the prime mover. The drive sprocket of the presentinvention provides an eflicient driving means which is light weight andin which the driving pins, the elements having the greatest wear, arereadily replaceable.

What is claimed is:

1.. In a portable chain saw including a chain having cutting links,guiding links, and connecting links and a prime mover, the improvementresiding in a drive sprocket comprising,

a sprocket body,

a pair of flanges extending radially outward from said body in parallelrelation to define an annular groove, and

driving pins extending across said annular groove and engaged in saidflanges,

said driving pins adapted to engage said chain to drive said chain,

said driving pins being positioned sufiiciently outward in said groovewhereby in operation, each of said pins when driving said chain, wouldengage a cutting link and its associated connecting link at a pointadjacent a guiding link with said guide link coacting with said pin tomaintain it in engagement with said cutting link and said connectinglink,

said flanges define an inner portion of said groove of suflicient widthto receive said guide link, an intermediate portion of said groove ofincreased width sufiicient to receive the whole width of the chain andan outer portion of said groove of increasing width and of sufficientdiameter to prevent inadvertent disengagement of said chain from saiddrive sprocket.

2. The drive sprocket according to claim 1 wherein,

said driving pins are loosely engaged in said flanges whereby said drivepins are free to rotate with said chain links.

3. In a portable chain saw including a chain having 0 cutting links,guiding links, and connecting links and a prime mover, the improvementresiding in a drive sprocket comprising,

a sprocket body, a-pair of flanges extending radially outward from saidbody in parallel relation to define an annular groove, and driving pinsextending across said annular groove and engaged in said flanges, saiddriving pins adapted to engage said chain to drive said chain, saiddriving pins being positioned sufliciently outward in said groovewhereby in operation, each of said pins when driving said chain, wouldengage a cutting link and its associated connecting link at a pointadjacent a guiding link with said guide link coacting with said pin tomaintain it in engagement with said cutting link and said connectinglink, said flanges define an inner portion of said annular groove ofsufiicient width only to receive said guide links, an intermediateportion of said annular groove having parallel radially extending sidesof suflrcient width to receive said chain and across which said pinsextend and an outer portion of said annular groove having graduallyincreasing width and sufficient diameter to provide surfaces maintainingsaid chain in engagement with said sprocket body.

References Cited UNITED STATES PATENTS 1,526,451 2/1925 Wolf 74-2432,854,294 9/1958 Bannister 74-243 X 2,884,798 5/1959 Wilson 74-2433,279,272 10/ 1966 Gudmundsen 74-243 FRED C. MATTERN, J R., PrimaryExaminer.

DAVID J. WILLIAMOWSKY, Examiner.

I. A. WONG, Assistant Examiner.

1. IN A PORTABLE CHAIN SAW INCLUDING A CHAIN HAVING CUTTING LINKS,GUIDING LINKS, AND CONNECTING LINKS AND A PRIME MOVER, THE IMPROVEMENTRESIDING IN A DRIVE SPROCKET COMPRISING, A SPROCKET BODY, A PAIR OFFLANGES EXTENDING RADIALLY OUTWARD FROM SAID BODY IN PARALLEL RELATIONTO DEFINE AN ANNULAR GROOVE, AND DRIVING PINS EXTENDING ACROSS SAIDANNULAR GROOVE AND ENGAGED IN SAID FLANGES, SAID DRIVING PINS ADAPTED TOENGAGE SAID CHAIN TO DRIVE SAID CHAIN, SAID DRIVING PINS BEINGPOSITIONED SUFFICIENTLY OUTWARD IN SAID GROOVE WHEREBY IN OPERATION,EACH OF SAID PINS WHEN DRIVING SAID CHAIN, WOULD ENGAGE A CUTTING LINKAND ITS ASSOCIATED CONNECTING LINK AT A POINT ADJACENT A GUIDING LINKWITH SAID GUIDE LINK COACTING WITH SAID PIN TO MAINTAIN IT IN ENGAGEMENTWITH SAID CUTTING LINK AND SAID CONNECTING LINK, SAID FLANGES DEFINE ANINNER PORTION OF SAID GROOVE OF SUFFICIENT WIDTH TO RECEIVE SAID GUIDELINK, AN INTERMEDIATE PORTION OF SAID GROOVE OF INCREASED WIDTHSUFFICIENT TO RECEIVE THE WHOLE WIDTH OF THE CHAIN AND AN OUTER PORTIONOF SAID GROOVE OF INCREASING WIDTH AND OF SUFFICIENT DIAMETER TO PREVENTINADVERTENT DISENGAGEMENT OF SAID CHAIN FROM SAID DRIVE SPROCKET.